The present invention relates to a method and apparatus used for processing color images from a sequentially illuminated object to form high resolution color video signals suitable for use in viewing the object on a television monitor.
It will be appreciated by those skilled in the art that the use of charge coupled devices (CCD) as sensors in video imaging systems has become quite popular, as, for example, where small size and low power consumption is desired. In the processing of color video images, it is preferred for a number of reasons that a single CCD sensor be used. To that end, several methods have been developed in the prior art, one class of which requires sequential illumination of the object to be viewed, and subsequent processing of signals from the sensor which represent the level of reflected light corresponding to each of three primary colors.
Prior art sequential illumination and processing methods, however, are deficient in either the level of resolution obtainable, in their need for a higher rate of sampling of data from the sensor, or in their relative sensitivity. For example, in U.S. Pat. No. 4,253,447 is disclosed a sequential illumination process which requires reading out of only half the field lines (corresponding to either the even or the odd fields), resulting in a 50% reduction in vertical resolution. The '447 patent also discloses a second method whereby the object is sequentially illuminated by all three primary colors during each of the odd and even field periods. Unfortunately, this method requires that the CCD data be read at three times the standard speed which is not always possible. In addition, this technique requires six field memories and for a given signal-to-noise ratio, it is less sensitive than the current invention by a factor of three.
Prior art light sources used in conjunction with a sequential color video camera include: sequentially lighting the object field with each primary color by rotating a three-color segmented filter in the path of a white light source; sequentially illuminating the object with a plurality of solid state light emitting chips mounted in a single transparent package, as disclosed in U.S. Pat. No. 4,074,306; or sequentially illuminating the object with three white strobe lights with a different primary color filter in each of the strobe light paths, as shown in U.S. Pat. No. 4,253,447. All of these methods are troublesome.
In some instances it is difficult or inconvenient to cable video information to a monitor, yet it is desirable to transmit color video data to a remote site for display and analysis. It is also in many cases desirable to minimize the amount of circuitry at the sensor site for applications such as minimum invasion (laparoscopic) surgery, drill hole inspections, and the like.
What is needed, then, is an apparatus for sequentially illuminating an object and processing color images therefrom, using a single sensor and a minimum of memory devices, and a flicker-free method of processing video signals from the sensor without degradation of spatial resolution or sensitivity, and without the need for accelerated sampling rates. Preferably, this apparatus should also be adaptable to applications which would benefit from remote transmission of video data.